The present invention relates generally to microfluidic devices having one or more microchannels formed on a substrate, and specifically to optical or fluid interconnections formed to microfluidic devices, to microfluidic devices incorporating such interconnections, and to a process for forming the same.
Microfluidic devices are being developed for many applications including micro analysis systems, micromechanical actuators, localized or global substrate cooling, and ink-jet printing. Micro analysis systems which utilize microminiature fluid channels include liquid and gas chromatography, electrophoresis, free-flow fractionation, and polmerase chain reaction.
Conventional methods for forming interconnections to microfluidic devices are largely based on piece-part assembly with microcapillary tubing being oriented perpendicular to a backside of a substrate containing the microfluidic device and connected to a microchannel through a hole formed through the substrate (see e.g. U.S. Pat. No. 6,096,656 to Matzke et al, which is incorporated herein by reference). The microcapillary tubing is attached to the substrate using an adhesive which is disposed in the hole through the substrate. In some cases, the microcapillary tubing can be initially attached to small pieces of glass having machined thru-holes which are then attached to the backside of the substrate using an adhesive or anodic bonding.
The present invention provides an improvement over the prior art by forming external interconnections using microcapillary tubing or optical fibers which are oriented substantially parallel to an upper surface of the substrate whereon the microfluidic device is formed.
The present invention allows the external interconnections to be precisely aligned with one or more microchannels within a microfluidic device, and to be formed during or after formation of the microchannels using processes which are compatible with formation of the microchannels.
These and other advantages of the present invention will become evident to those skilled in the art.
The present invention relates to a microfluidic device comprising a substrate having at least one microchannel formed therein, with at least one external interconnection to the microchannel being formed substantially parallel to a surface of the substrate by a microcapillary tubing or an optical fiber located within an elongate trench formed in the substrate proximate to the microchannel and connected thereto, and with a covering layer comprising silicon oxynitride being deposited over the substrate to cover the trench and thereby adhere, at least in part, the microcapillary tubing or optical fiber to the substrate. The microcapillary tubing or optical fiber is generally further adhered to the substrate by an adhesive disposed within the trench. The covering layer also forms a fluid-tight seal between the microchannel and the external interconnection which is sealed at its sides and bottom to the trench with the adhesive.
The trench can be formed with sidewalls that are oriented substantially perpendicular to the surface of the substrate, or at oblique angles to the surface. One end of the trench proximate to the microchannel can be optionally graded to accommodate microcapillary tubing which is larger than the microchannel.
A barrier layer (e.g. comprising silicon dioxide) can be provided on one or both sides of the silicon oxynitride layer for improved resistance to moisture or chemical attack.
The substrate can comprise a material such as a semiconductor (e.g. silicon), crystalline quartz, fused silica, glass, ceramic, a polymer or a metal. In some instances an electrically-insulating substrate is preferred, for example, when high voltages are provided to the microfluidic device to provide an electrophoretic, electrokinetic or electroosmotic flow therein.
The present invention further relates to an optical or fluidic interconnection to a microchannel formed in a substrate. The interconnection comprises an elongate trench formed in the substrate proximate to the microchannel and connected thereto, with the trench being aligned substantially parallel to a surface of the substrate wherein the microchannel is formed. The interconnection further comprises a microfluidic tubing or optical fiber located within the trench and adhered to the sides and bottom of the trench with an adhesive disposed in the trench, and a fluid-tight covering formed over at least a portion of the trench, with the fluid-tight covering comprising a layer of silicon oxynitride.
The interconnection can be formed to microfluidic devices fabricated on many different types of substrates as described above; and the trench can be formed with sidewalls that are substantially perpendicular to the surface of the substrate, or oriented at oblique angles thereto. The trench can also be graded at one end thereof proximate to the microchannel, if needed.
A barrier layer can be provided on one or both sides of the silicon oxynitride layer to improve the resistance to moisture and prevent chemical attack (e.g. corrosion). The barrier layer, if used, generally comprises silicon dioxide.
The present invention also relates to a method for forming an interconnection to a microchannel on a substrate that comprises forming (e.g. by etching) an elongate trench below a surface of the substrate near an edge thereof proximate to the microchannel, with the trench being sized to receive one end of a microcapillary tubing or an optical fiber, and with one end of the trench being connected to the microchannel; adhering the end of the microcapillary tubing or optical fiber within the trench with an adhesive (e.g. an epoxy which can be cured using ultraviolet light); depositing a sacrificial material (e.g. a photoresist or a photodefinable polymer) within a portion of the trench not occupied by the microcapillary tubing or optical fiber; depositing a layer of silicon oxynitride over the surface of the substrate, with the layer of silicon oxynitride forming a fluid-tight covering over the trench and over the end of the microcapillary tubing or optical fiber located within the trench; and removing (e.g. by dissolution using a solvent) the sacrificial material from the trench. This method is particularly useful for forming interconnections to microfluidic devices when the microchannel is pre-existing on the substrate. An optional step can be provided for forming a barrier layer on one or both sides of the silicon oxynitride layer, if needed, to improve resistance to moisture and chemical attack.
In some instances, the present invention can be used to form the interconnections and microchannels at the same time and using the same series of process steps. This can be done with a simple modification of the above method by forming a microchannel on the substrate, and forming at least one elongate trench connected to the microchannel, with each trench being located near an edge of the substrate and being sized to receive one end of a microcapillary tubing or optical fiber; adhering the end of the microcapillary tubing or optical fiber within the trench with an adhesive; depositing a sacrificial material within the microchannel and within a portion of the trench not occupied by the microcapillary tubing or optical fiber; depositing a layer of silicon oxynitride over the surface of the substrate, with the layer of silicon oxynitride forming a fluid-tight covering over the microchannel and the trench, and over the end of the microcapillary tubing or optical fiber located within the trench; and removing the sacrificial material from the microchannel and trench.
Additional advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following detailed description thereof when considered in conjunction with the accompanying drawings. The advantages of the invention can be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.